A light emitting diode is a photoelectric transformation semiconductor element in which an N-type semiconductor and a P-type semiconductor are joined together to form a junction and electrons and holes are re-combined to emit light. Such light emitting diodes are widely used as a display device and a backlight. In addition, the light emitting diode consumes less electric power as compared with conventional in-candescent bulbs or fluorescent lamps, and has an extended service life, thereby broadening its applications to general illumination purposes while replacing the conventional incandescent bulbs and fluorescent lamps.
The light emitting diode alternates between on- and off-states under an AC power source, depending on the direction of a current applied thereto. Therefore, if the light emitting diode is connected directly to an AC power source, there are problems in that it cannot emit light in a continuous mode and may be easily damaged due to a reverse current.
As an attempt to solve the above problems in the art, Sakai et al. proposed a light emitting diode capable of being connected directly to a high voltage AC power source, which is disclosed in International Publication No. WO 2004/023568A1 entitled “Light-Emitting Device Having Light-Emitting Elements.
In the publication WO 2004/023568A1, LEDs are serially connected in a two-dimensional pattern on an insulation substrate such as a sapphire substrate to form LED arrays. Two LED arrays are connected in reverse parallel on the sapphire substrate. Consequently, a single chip light emitting device that can be driven by the AC power source is provided.
However, since the sapphire substrate has a relatively low thermal conductivity, heat cannot be smoothly dissipated. This limited heat dissipation leads to a limited maximum light output of the light emitting device. Therefore, there is a need for a continuous effort to improve the maximum light output of a light emitting device under a high voltage AC power source.